Volvo 3.0 GSP-A high idle

[fcawth]

I am getting the boat ready for the next season, and I still have a nagging issue left over from last year. The boat is a 2001 Larson with a Volvo 3.0 GSP-A and SX drive. Last year was my first season with it. It has been hard to get the thing to idle at low RPMs, and I have to have the throttle plates pretty much jammed closed to get it down to 650. The idle screw was backed all the way off when I bought the boat (did not realize until later).

It has a holley 2 barrel carb, and I replaced the carb with a rebuilt one (same model) and had the same issue. I tried to use propane to search for a vacuum leak, but the only leak I can find is around the throttle shafts. I also replaced the throttle plates with some from Holley that didn't have the small holes. This helped a little.

I have checked the timing (with the shunt - it was right on).

I replaced the PCV valve.

Now I can get it to idle at 650-700 when just warmed up with just slightly cracked open throttle plates. The problem is after I run at speed for a while, the idle is up at 850-900 or so. The carb guy said that this might be because the plates are so far closed that the carb body expands more than the steel plates and lets in a bit more air. If I set it to idle at 750 when hot, then it idles rough at about 500-550 (and almost dies) when cold/warm.

So... Now I'm not sure what to check next. Any ideas? What does the PCV valve do anyway, should I just close it off? (The other end of the crankcase is basically a big hole where the vent goes up to the flame arrestor, so there is no way the crankcase is going to be put under vacuum by the PCV valve anyway). Doesn't the PCV valve act just like a vacuum leak in this case?

I was going to pull the manifold (I even have a new gasket). BUT, there is a stud (not bolt) right behind the exhaust pipe, so it looks like the engine needs to be pulled to get the manifold off. What's the deal with that?? Are there any tricks there?

The only other thing is that there were bits of impeller in one of the water hoses when I bought the boat, and so it might have run hot at some point. Now it runs right at temperature, and seems to run at the appropriate WOT RPMS, etc. Perhaps the manifold was warped and there is an exhaust to intake leak?



Thanks for any help/suggestions/ideas.

Fred

 

[Don S]

Re: Volvo 3.0 GSP-A high idle

After the engine warms up, disconnect the throttle cable from the carb and see if you can adjust the idle speed. If it dies, adjust the idle speed up until it keeps running, get it to the proper rpm, then adjust the throttle cable end so there is a slight preload to the idle position. Notice, I said light preload.

 

[fcawth]

Re: Volvo 3.0 GSP-A high idle

Thanks for the quick reply Don.

I actually forgot to mention that I already have a slight preload on the throttle cable closing the arm down against the idle screw. This was also there when I bought the boat (so someone was working on this before I bought the boat).

Is there anything major (valves?) that could cause this?

When I checked manifold vacuum with a vac. gauge, it was in the range in the volvo manual (I forget the number but it didn't seem low), and it was steady.

Are there issues with these carbs? There seem to be lots of carb changes since 2001.

Thanks,
Fred

 

[Don S]

Re: Volvo 3.0 GSP-A high idle

What is your engine serial number?

 

[fcawth]

Re: Volvo 3.0 GSP-A high idle

Here's the info from the engine:

Prod. # 3869106
3.0GSP-A
S/N 4012041306

Thanks again Don.

Fred

 

[Don S]

Re: Volvo 3.0 GSP-A high idle

No known problems for your SN. All the carb problems were years after your SN and wouldn't cause your problem anyway.
Since you do have a Holley carb, if you have had any backfires, you may have a blown power valve that could be feeding excess fuel to the engine, and may take more air to keep it running. That would equate to higher idle rpm.

 

[fcawth]

Re: Volvo 3.0 GSP-A high idle

Well, I just pulled the manifold and replaced the gasket. It is possible I had a slight leak there (there was fogging oil down on the gasket but it might have leaked down there as I took it off) . I put a small amount of avation gasket compound on the new gasket, so if there was any leak before, there isn't now. At least it was nice to see that the manifold and riser were both in great shape, and I could inspect the top of the valves which didn't look too bad. Overall, it took me alot less time than I was thinking it would (maybe 3-4 hours, but I was very careful scraping off every speck of old gasket, etc)



For anyone else needing to pull the manifold on a 3.0 volvo with the exhaust pipe in the way, you can just barely get the thing off (and I mean just barely- it might not work in every case) if you unthread the stud while the manifold is still on (I used the nut from the other stud to lock the nuts together and loosen the stud, then I had to take the second nut off to get enough room). The threads come out of the block right as the stud hits the exhaust pipe. You can then slide the manifold up in the back until it clears the exhaust pipe and then slide it off the front stud. WHY they didn't put in a bolt in that rear location I don't know (they are smaller diameter threads than the regular bolts, but still..). If I had the right bolt, I would have replaced the rear stud with a bolt when reassembling, so if you are planning this you can probably have one ready... Everything on mine was in really good shape (fresh water only), so if you have lots of corrosion you might have more trouble.

As far as my idle goes, I still have the drive off for the winter, so we'll see in a few weeks...


Thanks again to Don for the input.

Fred